Musnad Ahmad 1153:597

Qutaybah narrated to us, Yahya—meaning Ibn Zakariyya—narrated to us, from his father, from Mus'ab ibn Shaybah, from Musafi' ibn 'Abd Allah al-Hajabi, from 'Urwah ibn al-Zubayr, from 'Aishah, that a woman said to the Prophet, peace and blessings of Allah be upon him: "Does a woman have to perform ghusl (ritual bath) if she has a wet dream and sees the fluid?" He said: "Yes." 'Aishah said to her: "May your hands be covered in dust!" The Prophet, peace and blessings of Allah be upon him, said: "Leave her. And is the resemblance [of the child] from anything other than that? If her fluid overcomes the man's fluid, the child resembles its maternal uncles, and if the man's fluid overcomes her fluid, it resembles him."